That is also my impression as well. The softwareization of trains has led to deep regressions in both basic reliability and interoperability/flexilibity. Many modern trains suffer from software issues for basic driving [0] and delays when getting the software approved [1]. But the loss of compatability is in my opinion the worst regression. Modern EMUs basically only work together with other EMUs of the same batch. Even the same model ordered by two different companies often don't work together and basically forget about trying to use EMUs of different companies or ordered over a decade apart together. Meanwhile pre-digital everything it was common to use e.g. trams of different generations together and rewire them to work with each other. Older train cars work together without issues, good luck trying to use an IC2 and a Railjet together (or a RailJet and ICE-L). Even certain locomotives and train cars would often only work with each other.

It is way harder for different computerized systems to work together due to the higher complexity and more obfuscation (a traditional logic circuitboard is often easily reverse engineered. Reverse engineering software is a very specialized task). This is also very noticeable in other sectors, where interoperability has become much worse due to moving to proprietary digital protocols.

This is in part due to the difficulty in getting software approved as compared to previous tech (due to software being so intransparent) but also because of truly lacking quality. One of the reasons Bombardier was so deep in trouble was bad software, even leading to a contract of over 40 ordered trains just being cancelled ([2]).

In my opinion building reliable (and understandable) software is way harder than building logic or even mechanical systems. I don't know what the solution is, but it's been a problem for a long time.

[0]: https://www.vrt.be/vrtnws/de/2013/02/12/belgische_bahn_storn... [1]: https://www.augsburger-allgemeine.de/augsburg/Neue-Zuege-auf... [2]: https://de.wikipedia.org/wiki/Bombardier_Talent_3#%C3%96BB